Driving circuit of a semiconductor display device and the semiconductor display device

ABSTRACT

There are provided a driving circuit of a semiconductor display device which can obtain an excellent picture without picture blur (display unevenness) and with high fineness/high resolution, and the semiconductor display device. A buffer circuit used in the driving circuit of the semiconductor display device is constituted by a plurality of TFTs each having a small channel width, and a plurality of such buffer circuits are connected in parallel with each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving circuit of an active matrixtype semiconductor display device. The present invention also relates tothe semiconductor display device having the driving circuit.

2. Description of the Related Art

In recent years, a technique for manufacturing a semiconductor devicehaving a semiconductor thin film formed on an inexpensive glasssubstrate, such as a thin film transistor (TFT), has been rapidlydeveloped. The reason is that the demand for an active matrix typesemiconductor display device (especially an active matrix type liquidcrystal display device) has been increased.

In the active matrix type liquid crystal display device, a TFT isdisposed for each of several tens to millions of pixels arranged inmatrix, and an electrical charge going in and out each pixel electrodeis controlled by a switching function of the TFT.

Especially, with the improvement of a display device in resolution andpicture quality, attention comes to be paid to an active matrix typeliquid crystal display device having a digital driving circuit which canprocess digital video data as it is.

In a source signal line side driving circuit of a semiconductor displaydevice including a digital driving circuit, digital video data suppliedfrom the outside are sequentially held by a latch circuit or the likefor a short time on the basis of a timing signal from a shift register.And after the data are converted into an analog signal (gradationvoltage), the signal is supplied to a corresponding pixel TFT. When thedigital driving circuit is used, it becomes possible to realize aso-called line-sequential driving in which pixel TFTs for one line aredriven at the same time.

In the digital driving circuit, on the basis of the timing signal fromthe shift register, operation timing of the latch circuit, D/Aconversion circuit, and the like is determined. A number of circuits andelements each having a large load capacity are connected to a signalline to which the timing signal is supplied from the shift register.Thus, there is a case that the timing signal from the shift registerproduces “dulling” on the way. As one of countermeasures to this, atrial has been made in which the timing signal from the shift registeris made to pass through a buffer circuit or the like to eliminate“dulling”.

If current capacity of a buffer circuit is small, the buffer function ismeaningless. So, a buffer having a large current capacity to a certaindegree is required. In the case where a buffer having a large currentcapacity is formed using thin film transistors, a TFT having a largecurrent capacity, that is, a large channel width is required. However,in a TFT having a large channel width, fluctuation in crystallinityoccurs in a component, and as a result, fluctuation in threshold voltageoccurs for each TFT. Thus, it is inevitable that fluctuation occurs alsoin the characteristics of a buffer constituted by a plurality of TFTs.Thus, there exist buffers having fluctuation in the characteristics foreach signal line, and the fluctuation in the characteristics directlycauses fluctuation in applied voltage to a pixel matrix circuit. Thiscauses display blur (display unevenness) of the display device as awhole.

Moreover, if the size (channel width) of a TFT is too large, only thecenter portion of the TFT functions as a channel, and its ends do notfunction as the channel. In this case, deterioration of the TFT isaccelerated.

Further, when the size of a TFT is large, self heat generation of theTFT becomes large, which sometimes causes chance of a threshold value ordeterioration.

In a gate signal line side driving circuit as well, a scanning signal issequentially supplied to a gate signal line (scanning line) on the basisof a timing signal from a shift register. In a digital driving circuitcarrying out line-sequential driving, all pixel TFTs for one lineconnected to one scanning line must be driven, and a load capacityconnected to one scanning line is large. Thus, also in the gate signalline side driving circuit, it is necessary to eliminate “dulling” bymaking the timing signal from the shift register pass through a buffercircuit or the like. Also in this case, since a buffer having a largecurrent capacity becomes necessary, the above described problems come tooccur. Especially, the buffer of the gate signal line must drive all ofthe connected TFTs for one line in the pixel matrix circuit, so that thefluctuation in the characteristics of the buffer makes remarkablepicture unevenness. This is one of the most serious problems when adisplay device with high fineness/high resolution is desired.

SUMMARY OF THE INVENTION

The present invention has been made to overcome the foregoing problems,and an object thereof is to provide a semiconductor display device whichcan eliminate picture blur (display unevenness) and can obtain anexcellent picture with high fineness/high resolution.

According to a mode of carrying out the present -invention, in a drivingcircuit of a semiconductor display device, as a TFT constituting abuffer circuit provided between a shift register circuit and a latchcircuit of a source signal line side driving circuit, a TFT having alarge size (channel width) is not used, but instead thereof, a pluralityof TFTs each having a small size and are connected in parallel with eachother are used. Moreover, as a TFT constituting a buffer circuitprovided between a shift register circuit and a gate signal line of a sgate signal line side driving circuit, a TFT having a large size(channel width) is not used, but instead thereof, a plurality of TFTseach having a small size and are connected in parallel with each otherare used. In both cases, a plurality of buffer circuits are connected inparallel with each other to constitute a buffer circuit portion in adriver circuit. By doing so, it is possible to reduce fluctuation incharacteristics of the buffer circuit while securing the currentcapacity thereof.

The structure of the present invention will be described hereinafter.

According to one aspect of the present invention, there is provided adriving circuit of a semiconductor display device, comprising: a sourcesignal line side driving circuit; and a gate signal line side drivingcircuit, wherein the gate signal line side driving circuit includes abuffer circuit which buffers a timing signal from a shift registercircuit and includes a plurality of inverter circuits, and each of theinverter circuits is constituted by a plurality of inverters connected-in parallel with each other. By this, the above object can be achieved.

According to another aspect of the present invention, there is provideda driving circuit of a semiconductor display device, comprising: asource signal line side driving circuit; and a gate signal line sidedriving circuit, wherein the source signal line side driving circuitincludes a buffer circuit which buffers a timing signal from a shiftregister circuit and includes a plurality of inverter circuits, and eachof the inverter circuits is constituted by a plurality of invertersconnected in parallel with each other. By this, the above object can beachieved.

According to still another aspect of the present invention, there isprovided a driving circuit of a semiconductor display device,comprising: a source signal line side driving circuit; and a gate signalline side driving circuit, wherein the source signal line side drivingcircuit includes a buffer circuit which buffers a timing signal from ashift register circuit and includes a plurality of inverter circuits,and each of the inverter circuits is constituted by a plurality ofinverters connected in parallel with each other, and wherein the gatesignal line side driving circuit includes a buffer circuit which buffersa timing signal from a shift register circuit and includes a pluralityof inverter circuits, and each of the inverter circuits is constitutedby a plurality of inverters connected in parallel with each other. Bythis, the above object can be achieved.

According to still another aspect of the present invention, there isprovided a semiconductor display device, comprising: the driving circuitof the semiconductor display device according to each of the foregoingaspects of the present invention; and a pixel matrix circuit. By this,the above object can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a circuit block diagram of an active matrix type liquidcrystal display device including driving circuits according to anembodiment of the present invention;

FIG. 2 is a circuit diagram showing an embodiment of a digital videodata dividing circuit used for the driving circuit of the presentinvention;

FIG. 3 is a circuit diagram showing an embodiment of a portion of asource signal line side shrift register circuit and a portion of abuffer circuit used for the driving circuit of the present invention;

FIG. 4 is a circuit diagram showing an embodiment of an inverter usedfor the buffer circuit of the present invention;

FIG. 5 is a circuit diagram showing an embodiment of a portion of a gatesignal line side shift register circuit and a portion of a buffercircuit used for the driving circuit of the present invention;

FIG. 6 is a circuit diagram showing an embodiment of an inverter usedfor the buffer circuit of the present invention;

FIG. 7 is a circuit pattern diagram showing an embodiment of theinverter used for the driving circuit of the present invention;

FIG. 8 is a circuit pattern diagram showing an embodiment of theinverter used for the driving circuit of the present invention;

FIGS. 9A to 9D are views showing manufacturing steps of an active matrixtype liquid crystal display device including a driving circuit of thepresent invention;

FIGS. 10A to 10D are views showing manufacturing steps of the activematrix type liquid crystal display device including the driving circuitof the present invention;

FIGS. 11A to 11C are views showing manufacturing steps of the activematrix type liquid crystal display device including the driving circuitof the present invention;

FIG. 12 is a view showing the active matrix type liquid crystal displaydevice including the driving circuit of the present invention;

FIG. 13 is a view showing the outer appearance of an active matrix typeliquid crystal display device including a driving circuit of the presentinvention;

FIG. 14 is a view showing a TEM photograph of CGS;

FIG. 15 is a view showing a TEM photograph of a conventional hightemperature polysilicon;

FIGS. 16A and 16B are views showing electron beam diffraction patternsof CGS and conventional high temperature polysilicon;

FIGS. 17A and 17B are views showing TEM photographs of CGS andconventional high temperature polysilicon; and

FIGS. 18A and 18F are views showing semiconductor devices each includinga semiconductor display device having a driving circuit of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A driving circuit of a semiconductor display device and thesemiconductor display device according to the present invention will bedescribed below in detail in accordance with the following embodiments.However, the following embodiments are merely some embodiments of thepresent invention, and the driving circuit of the semiconductor displaydevice and the semiconductor device according to the present inventionare not limited thereto.

EMBODIMENT 1

In this embodiment, as an example in which a driving circuit of asemiconductor display device of the present invention is used, an activematrix type liquid crystal display device in which the number of pixelsis 1920×1080 in horizontal and vertical will be described.

Reference will be made to FIG. 1. FIG. 1 is a block diagram of a mainportion of an active matrix type liquid crystal display device of thisembodiment. The active matrix type liquid crystal display device of thisembodiment includes a source signal line side driving circuit A 101, asource signal line side driving circuit B 111, a gate signal line sidedriving circuit A 112, a gate signal line side driving circuit B 115, apixel matrix circuit 116, and a digital video data dividing circuit 110.

The source signal line side driving circuit A 101 includes a shiftregister circuit 102, a buffer circuit 103, a latch circuit (1) 104, alatch circuit (2) 105, a selector circuit (1) 106, a level shiftercircuit 107, a D/A conversion circuit 108, and a selector circuit (2)109. The source signal line side driving circuit A 101 supplies apicture signal (gradation voltage signal) to an odd-numbered sourcesignal line.

The operation of the source signal line side driving circuit A 101 willbe described. A start pulse and a clock signal are inputted to the shiftregister circuit 102. The shift register circuit 102 sequentiallysupplies a timing signal to the buffer circuit 103 based on the startpulse and the clock signal. Although described later, the shift registercircuit 102 is constituted by a plurality of clocked inverters.

The timing signal from the shift register circuit 102 is buffered by thebuffer circuit 103. A number of circuits or components are connectedbetween the shift register circuit 102 and a source signal lineconnected to the pixel matrix circuit 116, so that the load capacity islarge. In order to prevent “dulling” of the timing signal generatedsince the load capacity is large, this buffer circuit 103 is provided.

The timing signal buffered by the buffer circuit 103 is supplied to thelatch circuit (1) 104. The latch circuit (1) 104 includes 960 latchcircuits each processing 4-bit data. When the timing signal is inputtedin the latch circuit (1) 104, a digital signal supplied from the digitalvideo data dividing circuit 110 is sequentially taken in and is held bythe latch circuit.

A time up to the end of writing of digital signals into all latchcircuits of the latch circuit (1) 104 is called “one line period”. Thatis, one line period is a time interval from a time point when writing ofdigital video data from the digital video data dividing circuit isstarted for the leftmost latch circuit in the latch circuit (1) 104 to atime point when writing of digital video data is ended for the rightmostlatch circuit (1).

After the writing of the digital signals into the latch circuit (1) 104is ended, when a latch pulse is flown through a latch pulse lineconnected to the latch circuit (2) 105 synchronously with the operationtiming of the shift register circuit 102, the digital signals written inthe latch circuit (1) 104 are transmitted to the latch circuit (2) 105at the same time and are written.

In the latch circuit (1) 104 which completes transmission of the digitalvideo data to the latch circuit (2) 105, writing of digital video datasupplied from the digital video data dividing circuit is sequentiallycarried out again by the timing signal from the shift register circuit102.

During this second one line period, the digital video data transmittedto the latch circuit (2) synchronously with the start of the second oneline period are sequentially selected by the selector circuit (1) 106.The details of the selector circuit are disclosed in Japanese PatentApplication No. Hei 9-286098 filed on Oct. 1, 1997 by the presentassignee, which may be referred to. The entire disclosure of theJapanese Patent Application No. Hei 9-286098 including specification,claims, drawings and summary are incorporated herein by reference in itsentirety.

Four-Bit digital video data are supplied to the level shifter circuit107 from the latch circuit selected by the selector circuit. The voltagelevel of the digital video data is raised by the level shifter circuit107, and the data are supplied to the D/A conversion circuit 108. Thedetails of the D/A conversion circuit are disclosed in Japanese PatentApplications Nos. Hei 9-344,351 filed on Nov. 27, 1997 and Hei 9-365054filed on Dec. 19, 1997 by the present assignee, which may be referredto. The entire disclosures of the above Japanese Patent Applicationsincluding specifications, claims, drawings and summaries areincorporated herein by references in their entirety.

The D/A conversion circuit 108 converts the 4-bit digital video datainto an analog signal (gradation voltage), which is sequentiallysupplied to a source signal line selected by the selector circuit (2)109. The analog signal supplied to the source signal line is supplied toa source region of a pixel TFT of the pixel matrix circuit 116 connectedto the source signal line.

In the gate signal line side driving circuit A 112, a timing signal froma shift register 113 is supplied to a buffer circuit 114, and issupplied to a corresponding gate signal line (scanning line). Gateelectrodes of pixel TFTs for one line are connected to the gate signalline, and all pixel TFTs for one line must be turned ON at the sametime, so that the buffer circuit 114 having a large current capacity isused.

In this way, switching of the corresponding TFT is carried out by thescanning signal from the gate signal line side shift register, and theanalog signal (gradation voltage) from the source signal line sidedriving circuit is supplied to the pixel TFT so that liquid crystalmolecules are driven.

Reference numeral 111 denotes the source signal line side drivingcircuit B, and its structure is the same as the source signal line sidedriving circuit A 101. The source signal line side driving circuit B 111supplies a picture signal to an even-numbered source signal line.

Reference numeral 110 denotes the digital video data dividing circuit.The digital video data dividing circuit 110 is a circuit for decreasingthe frequency of digital video data inputted from the outside to afactor of 1/m. By dividing the digital video data, the frequency of asignal necessary for the operation of the driving circuit can also bedecreased to a factor of 1/m.

Here, the digital video data dividing circuit 110 of this embodimentwill be described in brief with reference to FIG. 2. Incidentally,Japanese Patent Application No. Hei 9-356238 filed on Dec. 8, 1997 bythe same assignee discloses that the digital video dividing circuit isintegrally formed on the same substrate as the pixel matrix circuit andother driving circuits. The above patent application discloses thedetails of the operation of the digital video data dividing circuit, andmay be referred to for understanding of the operation of the digitalvideo data dividing circuit of this embodiment. The entire disclosure ofJapanese Patent Application No. Hei 9-356238 including specification,claims, drawings and summary are incorporated herein by reference in itsentirety.

In FIG. 2, reference numeral 201 denotes a synchronous counter, and aclock signal (ck) and a reset pulse (reset) are inputted. In thisembodiment, digital video data of 80 MHz supplied from the outside isdivided into 8 pieces, so that digital video data of 10 MHz areproduced. Thus, sixteen D flip-flops 202 are connected as shown in FIG.2. The digital video data of 10 MHz produced by the digital video datadividing circuit 110 are supplied to the latch circuit (1) 104 asdescribed above.

Reference will be made to FIG. 1 again, and the operation of the gatesignal line side driving circuit will be described. Reference numeral112 denotes the gate signal line side driving circuit A. The gate signalline side driving circuit A 112 includes the shift register circuit 113and the buffer circuit 114. The shift register circuit 113 supplies atiming signal to the buffer circuit 114. The buffer circuit 114 buffersthe timing signal from the shift register circuit 113, and supplies itto the gate signal line (scanning line).

Reference numeral 115 denotes the gate signal line side driving circuitB, and has the same structure as the gate signal line side drivingcircuit A 112. In this embodiment, the gate signal line side drivingcircuits are provided in this way at both ends of the pixel matrixcircuit 116, and both the gate signal line side driving circuits areoperated, so that this embodiment can deal with even in the case whereone does not operate.

The pixel matrix circuit 116 has such a structure that pixel TFTs, thenumber of which is 1920×1080 in horizontal and vertical, are arranged inmatrix.

One screen (one frame) is formed by repeating the foregoing operation bythe number of the scanning lines. In the active matrix type liquidcrystal display device of this embodiment, updating of pictures of 60frames per second are carried out.

Here, a circuit diagram of a part (uppermost part) the shift registercircuit 102 and the buffer circuit 103 of this embodiment will be shownin FIG. 3. FIG. 3 shows a flip-flop (FF) circuit 102′ constituting theshift register circuit 102 and one portion of the buffer circuit 103′constituting the buffer circuit 103.

In this embodiment, the shift register circuit 102 is constituted by 240such flip-flop circuits 102′. The flip-flop circuit 102′ includesclocked inverters 301 to 304. Reference character ck denotes a clocksignal. Reference character LR denotes a scanning direction chargingsignal. When the signal LR is high, a start pulse (SP) is supplied tothe leftmost flip-flop circuit 102′ of the shift register circuit 102,and the flip-flop circuit 102′ transfers a signal from left to right.When the signal LR is low, a start pulse (SP) is supplied to therightmost flip-flop circuit (not shown), and the flip-flop circuit 102′transfers a signal from right to left.

Explanation will be made below on the case, as an example, where thesignal LR is a high signal, that is, the flip-flop circuits of the shiftregister circuit 102 operate from left to right.

A start pulse (SP) is inputted into the clocked inverter 301. When thestart pulse is inputted into the clocked inverter 301, the clockedinverter 301 operates synchronously with a clock signal (ck) and aninverted clock signal (inverted ck), and outputs an inverted signal ofan input signal. Since the signal LR (high) is inputted in the clockedinverter 302, the clocked inverter 302 receives the signal from theclocked inverter 301, and outputs its inverted signal. The clockedinverter 304 receives the signal from the clocked inverter 302, andoutputs its inverted signal. Since the signal LR (high) is inputted inthe clocked inverter 303, it does not operate. In this way, theflip-flop circuit 102′ outputs a timing signal to a NAND circuit 305.

The timing signal from the shift register circuit 102 (flip-flop circuit102′) passes through the NAND circuit 305 and is supplied to the oneportion of the buffer circuit 103′. In this embodiment, the one portionof the buffer circuit 103′ includes five inverters 306 to 310. Althoughthe one portion of the buffer circuit 103′ includes five inverters inthis embodiment, in the present invention, the number of inverters isnot limited to this, but may include inverters which are less than fiveor larger than five in number.

These five inverters 306 to 310 are respectively constituted by TFTswith different sizes (channel widths). In this embodiment, the inverters306, 307 and 308 are constituted by TFTs each having a channel width of30 μm. The inverters 309 and 310 are constituted by TFTs each having achannel width of 100 μm. An optimum size selected through simulation orthe like can be used for the size of the TFT constituting theseinverters. Besides, the optimum size of the TFT can be determinedaccording to the number of pixels of the semiconductor display device,or the like.

Here, explanation will be made using the inverter 307 as an example.FIG. 4 is a circuit diagram of the inverter 307. The inverter 307 isconstituted by six P-channel TFTs and six N-channel TFTs. The channelwidth of each of the TFTs is 30 μm. Incidentally, it is appropriate thatthe channel width of these TFTs is made 100 μm or less (preferably 90 μmor less).

As shown in FIG. 4, the inverter 307 has such a structure that twoinverter circuits are connected in parallel with each other, each of theinverter circuits being constituted by a circuit in which threeP-channel TFTs are connected in series with each other (triple gate TFTsare used in the circuit) and by a circuit in which three N-channel TFTsare connected in series with each other (triple gate TFTs are used inthe circuit). Like this, when plural lines of TFTs each having a smallchannel width (30 μm in this embodiment) are combined, as compared withthe case where an inverter is constituted by TFTs each having a largechannel width, fluctuation in the TFTs can be eliminated. Moreover, heatgeneration and deterioration due to the large channel width can beprevented.

Next, reference will be made to FIG. 5. FIG. 5 is a circuit diagramshowing a part (uppermost portion) of the shift register circuit 113 andthe buffer circuit 114 of the gate signal line side driving circuit A112 of this embodiment, and shows a flip-flop circuit 113′ constitutingthe shift resister circuit 113 and a portion of the buffer circuit 114′constituting the buffer circuit 114.

In this embodiment, the shift register circuit 113 is constituted by1080 such flip-flop circuits 113′. The flip-flop circuit 113′ includesclocked inverters 501 to 504. Reference character ck denotes a clocksignal. Reference character LR denotes a scanning direction changingsignal, and when the signal LR is high, a start pulse (SP) is suppliedto the leftmost flip-flop circuit 113′ of the shift register circuit113, and when the signal LR is low, the start pulse (SP) is supplied tothe rightmost flip-flop circuit (not shown).

Since the operation of the shift register circuit 113 is the same as theshift register circuit 102 of the source signal line side drivingcircuit, its explanation will be omitted.

A timing signal from the shift register circuit 113 (flip-flop circuit113′) passes through a NAND circuit 505, and is supplied to the oneportion of the buffer circuit 114′. The one portion of the buffercircuit 114′ includes three inverters 506 to 508. In this embodiment,although the one portion of the buffer circuit 114′ includes threeinverters, in the present invention, the number of inverters is notlimited to this, but may include inverters which are less than three orlarger than three in number.

These three inverters 506 to 508 are constituted by TFTs each having achannel width of 90 μm. An optimum size selected through simulation orthe like can be used for the size of the TFT constituting theseinverters. Besides, the optimum size of the TFT can be determinedaccording to the number of pixels of the semiconductor display device,or the like.

FIG. 6 is a circuit diagram of the inverter 508. The inverter 508 isconstituted by eight P-channel TFTs and eight N-channel TFTs. Thechannel width of each of the TFTs is 90 μm. It is appropriate that thechannel width of these TFTs is 100 μm or less (preferably 90 μm orless).

As shown in FIG. 6, two circuits are connected in parallel with eachother, each circuit being constituted by two P-channel TFTs connected inseries with each other (actually, double gate TFTs are used). Moreover,two circuits are connected in parallel with each other, each circuitbeing constituted by two N-channel TFTs connected in series with eachother (actually, double gate TFTs are used). The inverter 508 isconstituted by these circuits. Like this, when a plurality of TFTs eachhaving a small channel width are combined, as compared with the casewhere an inverter is constituted by TFTs each having a large channelwidth, fluctuation in the TFTs can be eliminated and current capacitycan be secured. Moreover, heat generation and deterioration due to thelarge channel width can be prevented.

FIG. 7 is a circuit pattern diagram of the inverter 307 shown in FIG. 4.In FIG. 7, reference numerals 701 and 702 denote semiconductor activelayers added with N-type impurities. Reference numerals 703 and 704denote semiconductor active layers added with P-type impurities.Reference numeral 705 denotes a gate electrode wiring line and Al(aluminum) including Sc (scandium) of 2 wt % is used in this embodiment.Reference numerals 708 to 711 denote second wiring lines and Al is usedin this embodiment. Reference numeral 712 denotes a wiring line existingin the same layer as the gate electrode wiring line. A blackened portiontypically denoted by 713 is a portion where the gate electrode isconnected to the second wiring line, or the semiconductor active layeris connected to the second wiring line.

Reference numeral 706 denotes a GND, 707 denotes a VddH (power source),712 denotes an OUT (output), and 714 denotes an IN (input).

In the drawing, it is assumed that wiring lines with the same patternexist in the same wiring line layer. A portion indicated by a brokenline in the drawing shows the shape of a lower wiring line concealed byan upper wiring line.

In the inverter 307 shown in FIG. 7, although three P-channel TFTs andthree N-channel TFTs are formed on the same semiconductor layer, it isalso possible to adopt such a structure that three independent P-channelTFTs and three independent N-channel TFTs are formed on independentsemiconductor layers, and are connected to each other by metal wiring orthe like through contacts. However, the structure of this embodiment ispreferable since the area of the inverter 307 can be made smaller.

Next, reference will be made to FIG. 8. FIG. 8 is a circuit patterndiagram of the inverter 508 shown in FIG. 6. In FIG. 8, in addition tothe inverter 508, four inverters in total are shown.

In FIG. 8, reference numerals 801 to 808 denote semiconductor activelayers added with P-type impurities. Reference numerals 809 to 816denote semiconductor active layers added with N-type impurities.Reference numerals 817 to 824 denote gate electrode wiring lines, and Al(aluminum) including Sc (scandium) of 2 wt % is used in this embodiment.Reference numerals 825 to 828 denote wiring lines existing in the samelayer as the gate electrode wiring lines. Reference numerals 829 to 835denote second wiring lines, and Al is used in this embodiment. Ablackened portion typically denoted by 836 is a portion where the gateelectrode is connected to the second wiring line, or the semiconductoractive layer is connected to the second wiring line.

Reference numeral 829 denotes a VddH (high voltage power source), 832denotes a GND, and 833 denote a VddL (low voltage power source).Incidentally, each of reference characters IN1 to IN4 denote an input,and each of OUT1 to OUT4 denote an output.

In the drawing, wiring lines with the same pattern are made of the samematerial and exist on the same wiring layer. A portion indicated by abroken line in the drawing shows the shape of a lower wiring lineconcealed by an upper wiring line.

Here, a manufacturing method of an active matrix type liquid crystaldisplay device including the driving circuit of this embodiment will bedescribed. Incidentally, the manufacturing method described below is onemanufacturing method which realizes the present s invention, and theactive matrix type liquid crystal display device of the presentinvention can be realized by other manufacturing methods.

Here, an example in which a plurality of TFTs are formed on a substratehaving an insulating surface, and a pixel matrix circuit, a drivingcircuits a logic circuit, and the like are monolithically formed, willbe described with references to FIGS. 9 to 12. In this embodiment, astate in which one pixel of a pixel matrix circuit and a CMOS circuit asa basic circuit of other circuits (driving circuit, logic circuit, etc.)are formed at the same time, will be shown. In this embodiment, althoughmanufacturing steps will be described for the case where each of aP-channel TFT and an N-channel TFT includes one gate electrode, a CMOScircuit of TFTs each having a plurality of gate electrodes, such as adouble gate type or a triple gate type TFT, can also be manufactured inthe same way.

Reference will be made to FIGS. 9A to 9D. First, a quartz substrate 901is prepared as a substrate having an insulating surface. Instead of thequartz substrate, a silicon substrate on which a thermal oxidation filmis formed may be used. Moreover, such a method may be adopted that anamorphous silicon film is temporarily formed on a quartz substrate andthe film is completely thermally oxidized to form an insulating film. Inaddition, a quartz substrate or a ceramic substrate each having asilicon nitride film formed as an insulating film may be used.

An amorphous silicon film 902 is formed on the substrate 901 by a lowpressure CVD method, a plasma CVD method, or a sputtering method.Adjustment is made so that the final film thickness (film thicknessdetermined after paying consideration to a film decrease subsequent tothermal oxidation) of the amorphous silicon film 902 becomes 10 to 100nm (preferably 30 to 60 nm). In the film s formation, it is important tothoroughly manage the concentration of impurities in the film.

In this embodiment, although the amorphous silicon film 902 is formed onthe substrate 901, another semiconductor thin film may be used insteadof the amorphous silicon film. For example, it is also possible to use acompound of silicon and germanium indicated by Si_(X)Ge_(1-X) (0<X<1).

In the case of this embodiment, management is made so that theconcentration of each of C (carbon) and N (nitrogen), which areimpurities to block crystallization in the amorphous silicon film 902,becomes less than 5×10¹⁸ atoms/cm³ (typically, 5×10¹⁷ atoms/cm³ or less,preferably 2×10¹⁷ atoms/cm³ or less), and the concentration of O(oxygen) becomes less than 1.5×10¹⁹ atoms/cm³ (typically 1×10¹⁸atoms/cm³ or less, preferably 5×10¹⁷ atoms/cm³ or less). This is becauseif the concentration of any one of the impurities exceeds the abovevalue, the impurity may have a bad influence on subsequentcrystallization and may degrade a film quality after thecrystallization. In the present specification, the foregoingconcentration of the impurity element in the film is defined as aminimum value in measurement results of SIMS (Secondary Ion MassSpectroscopy).

In order to obtain the above structure, it is desirable to periodicallycarry out dry cleaning of a low pressure thermal CVD furnace used inthis embodiment so that a film growth chamber is made clean. It isappropriate that the dry cleaning of the film growth chamber is carriedout by flowing a CIF₃ (chlorine fluoride) gas of 100 to 300 sccm intothe furnace heated up to about 200 to 400° C. and by using fluorineproduced by pyrolysis.

According to the knowledge of the present inventors, in the case wherethe temperature in the furnace is made 300° C. and the flow rate of theClF₃ (chlorine fluoride) gas is made 300 sccm, it is possible tocompletely remove an incrustation (including silicon as its mainingredient) with a thickness of about 2 μm in four hours.

The concentration of hydrogen in the amorphous silicon film 902 is alsoa very important parameter, and it appears that as the hydrogen contentis made low, a film with superior crystallinity is obtained. Thus, it ispreferable to form the amorphous silicon film 902 by a low pressure CVDmethod. A plasma CVD method may also be used if film forming conditionsare optimized.

It is effective to add an impurity element (element in group 13,typically boron, or element in group 15, typically phosphorus) forcontrolling a threshold voltage (V_(th)) of a TFT at film formation ofthe amorphous silicon film 902. It is necessary to determine the amountof addition in view of V_(th) in the case where the above impurity forcontrolling V_(th) is not added.

Next, the amorphous silicon film 902 is crystallized. A techniquedisclosed in Japanese Patent Unexamined Publication No. Hei 7-130652published on May 19, 1995 (filed on Oct. 29, 1993) is used as a meansfor crystallization. Although both means of embodiment 1 and embodiment2 disclosed in the publication may be used, in this embodiment, it ispreferable to use the technical content (described in detail in JapanesePatent Unexamined Publication No. Hei 8-78329 published on Mar. 22,1996, filed on Sep. 5, 1994) set forth in the embodiment 2 of thepublication. The entire disclosures of both Japanese Patent UnexaminedPublications Nos. Hei 7-130652 and Hei 8-78329 including specification,claims, drawings and summary, respectively, are incorporated herein byreferences in their entirety.

According to the technique disclosed in Japanese Patent UnexaminedPublication No. Hei 8-78329, a mask insulating film 903 for selecting anadded region of an element for facilitating crystallization of theamorphous silicon film is first formed. The mask insulating film 903 hasa plurality of openings for addition of the element for facilitatingcrystallization of the amorphous silicon film. Positions of crystalregions can be determined by the positions of the openings.

A solution including nickel (Ni) as the element for facilitatingcrystallization of the amorphous silicon film is applied by a spincoating method to form a Ni including layer 904. As the element, cobalt(Co), iron (Fe), palladium (Pd), germanium (Ge), platinum (Pt), copper(Cu), gold (Au), or the like may be used other than nickel (FIG. 9A).

As the foregoing adding step of the element for facilitatingcrystallization of the amorphous silicon film, an ion implantationmethod or a plasma doping method using a resist mask may also be used.In this case, since it becomes easy to decrease an occupied area of anadded region and to control a growth distance of a lateral growthregion, the method becomes an effective technique when a minute circuitis formed.

Next, after the adding step of the element is ended, dehydrogenating iscarried out at about 500° C. for 2 hours, and then, a heat treatment iscarried out in an inert gas atmosphere, hydrogen atmosphere, or oxygenatmosphere at a temperature of 500 to 700° C. (typically 550 to 650° C.,preferably 570° C.) for 4 to 24 hours to crystallize the amorphoussilicon film 902. In this embodiment, a heat treatment is carried out ina nitrogen atmosphere, at 570° C. and for 14 hours.

At this time, crystallization of the amorphous silicon film 902progresses first from nuclei produced in regions 905 and 906 added withnickel, and crystal regions 907 and 908 grown almost parallel to thesurface of the substrate 901 are formed. The crystal regions 907 and 908are respectively referred to as a lateral growth region. Sincerespective crystals in the lateral growth region are gathered in acomparatively uniform state, the lateral growth region has such anadvantage that the total crystallinity is superior (FIG. 9B).

Incidentally, even in the case where the technique set forth inembodiment 1 of the above-mentioned Japanese Patent UnexaminedPublication No. Hei 7-130652 is used, a region which can be called alateral growth region is microscopically formed. However, sinceproduction of nuclei occurs irregularly in the surface, it is difficultto control crystal grain boundaries.

After the heat treatment for crystallization is ended, the maskinsulating film 903 is removed and patterning is carried out, so thatisland-like semiconductor layers (active layers) 909, 910, and 911 madeof the lateral growth regions 907 and 908 are formed (FIG. 9C).

Here, reference numeral 909 denotes the active layer -of the N-channelTFT constituting the CMOS circuit, 910 denotes the active layer of theP-channel TFT constituting the CMOS circuit, and 911 denotes the activelayer of the N-channel TFT (pixel TFT) constituting the pixel matrixcircuit.

After the active layers 909, 910 and 911 are formed, a gate insulatingfilm 912 made of an insulating film including silicon is formed thereon(FIG. 9C).

Next, as shown in FIG. 9D, a heat treatment (gettering process for theelement for facilitating crystallization of the amorphous silicon film)for removing or reducing the element for facilitating crystallization ofthe amorphous silicon film (nickel) is carried out. In this heattreatment, a halogen element is made contained in a processingatmosphere and the gettering effect for a metallic element by thehalogen element is used.

In order to sufficiently obtain the gettering effect by the halogenelement, it is preferable to carry out the above heat treatment at atemperature exceeding 700° C. If the temperature is not higher than 700°C., it becomes difficult to decompose a halogen compound in theprocessing atmosphere, so that there is a fear that the gettering effectcan not be obtained.

Thus, in this embodiment, the heat treatment is carried out at atemperature exceeding 700° C., preferably 800 to 1000° C. (typically950° C.), and a processing time is made for 0.1 to 6 hours, typically0.5 to 1 hour.

In this embodiment, there is shown an example in which a heat treatmentis carried out in an oxygen atmosphere including hydrogen chlorine (HCl)of 0.5 to 10 vol % (in this embodiment, 3 vol %) at 950° C. for 30minutes. If the concentration of HCl is higher than the above-mentionedconcentration, asperities comparable to a film thickness are produced onthe surfaces of the active layers 909, 910 and 911. Thus, such a highconcentration is not preferable.

Although an example in which the HCl gas is used as a compound includinga halogen element has been described, one kind or plural kinds of gasesselected from compounds including halogen, such as typically HF, NF₃,HBr, Cl₂, ClF₃, BCl₂, F₂, and Br₂, may be used other than the HCl gas.

In this step, it is conceivable that nickel is removed in such a mannerthat nickel in the active layers 909, 910 and 911 is gettered by theaction of chlorine and is transformed into volatile nickel chloridewhich is released into the air. By this step, the concentration ofnickel in the active layers 909, 910 and 911 is lowered down to 5×10¹⁷atoms/cm³ or less.

Incidentally, the value of 5×10¹⁷ atoms/cm³ is the lower limit ofdetection in the SIMS (Secondary Ion Mass Spectroscopy). As the resultof analysis of TFTs experimentally produced by the present inventors,when the concentration is not higher than 1×10¹⁸ atoms/cm³ (preferably5×10¹⁷ atoms/cm³ or less), an influence of nickel upon TFTcharacteristics can not be ascertained. However, the concentration of animpurity in the present specification is defined as the minimum value inmeasurement results of the SIMS analysis.

By the above heat treatment, a thermal oxidation reaction progresses atthe interface between the gate insulating film 912 and the active layers909, 910 and 911, so that the thickness of the gate insulating film 912is increased by the thickness of a thermal oxidation film. When thethermal oxidation film is formed in this way, it is possible to obtainan interface of semiconductor/insulating film, which has very fewinterfacial levels. Moreover, there is also an effect to preventinferior formation (edge thinning) of the thermal oxidation film at theend of the active layer.

The gettering process of the element for facilitating crystallization ofthe amorphous silicon film may be carried out after the mask insulatingfilm 903 is removed and before the active layer is patterned. And also,the gettering process of the element for facilitating crystallization ofthe amorphous silicon film may be carried out after the active layer ispatterned. Besides, any gettering processes may be combined.

Incidentally, the gettering process of the element for facilitatingcrystallization of the amorphous silicon film can also be carried out byusing P (phosphorus). The gettering process by phosphorus may becombined with the foregoing gettering process. Only the getteringprocess by phosphorus may be used.

Further, it is also effective that after the heat treatment in theabove-mentioned halogen atmosphere is carried out, a heat treatmentapproximately at 950° C. for one hour is carried out in a nitrogenatmosphere to improve the film quality of the gate insulating film 912.

Incidentally, it is also ascertained by the SIMS analysis that thehalogen element, which was used for the gettering process, having aconcentration of 1×10¹⁵ to 1×10²⁰ atoms/cm³ remains in the active layers909, 910 and 911. Moreover, it is also ascertained by the SIMS analysisthat at that time, the foregoing halogen element with a highconcentration is distributed between the thermal oxidation film formedby the heat treatment and the active layers 909, 910 and 911.

As the result of the SIMS analysis for other elements, it wasascertained that the concentration of any of C(carbon), N (nitrogen), O(oxygen), and S (sulfur) as typical impurities was less than 5×10¹⁸atoms/cm³ (typically 1×10¹⁸ atoms/cm³ or less).

The lateral growth region of the thus obtained active layer has a uniquecrystal structure made of a collective of rod-like or flattened rod-likecrystals. The features of the unique crystal structure will be describedlater.

Next, reference will be made to FIGS. 10A to 10D. First, a not-shownmetal film including aluminum as its main ingredient is formed, andoriginals 913, 914 and 915 of subsequent gate electrodes are formed bypatterning. In this embodiment, an aluminum film including scandium of 2wt % is used (FIG. 10A).

Incidentally, a polycrystalline silicon film added with impurities maybe used for the gate electrode, instead of the aluminum film includingscandium of 2 wt %.

Next, by a technique disclosed in Japanese Patent Unexamined PublicationNo. Hei 7-135318 published on May 23, 1995 (filed on Nov. 5, 1993),porous anodic oxidation films 916, 917 and 918, nonporous anodicoxidation films 919, 920 and 921, and gate electrodes 922, 923 and 924are formed (FIG. 10B). The entire disclosure of Japanese PatentUnexamined Publication No. Hei 7-135318 including specification, claims,drawings and summary are incorporated herein by reference in itsentirety.

After the state shown in FIG. 10B is obtained in this way, the gateinsulating film 912 is next etched by using the gate electrodes 922, 923and 924, and the porous anodic oxidation films 916, 917 and 918 asmasks. Then the porous anodic oxidation films 916, 917 and 918 areremoved to obtain the state shown in FIG. 10C. Incidentally, referencenumerals 925, 926 and 927 in FIG. 10C denote gate insulating films afterprocessing.

Next, an adding step of an impurity element giving one conductivity iscarried out. As the impurity element, P (phosphorus) or As (arsenic) maybe used for an N-channel type, and B (boron) or Ga (gallium) may be usedfor a P-channel type.

In this embodiment, each of adding steps of impurities for forming anN-channel TFT and a P-channel TFT is divided into two steps and iscarried out.

First, the addition of impurities for forming the N-channel TFT iscarried out. The first impurity addition (P (phosphorus) is used in thisembodiment) is carried out at a high acceleration voltage of about 80 kVto form an n⁻ region. Adjustment is made so that the concentration ofthe P ion in the n⁻ region becomes 1×10¹⁸ atoms/cm³ to 1×10¹⁹atoms/cm³⁻.

Further, the second impurity addition is carried out at a lowacceleration voltage of about 10 kV to form an n⁺ region. Since theacceleration voltage is low at this time, the gate insulating filmfunctions as a mask. Adjustment is made so that the sheet resistance ofthe n⁺ region becomes 500 Ω or less (preferably 300 Ω or less).

Through the above described steps, a source region 928, a drain region929, a low concentration impurity region 930, and a channel formationregion 931 of the N-channel TFT constituting the CMOS circuit areformed. Moreover, a source region 932, a drain region 933, a lowconcentration impurity region 934, and a channel formation region 935 ofthe N-channel TFT constituting the pixel TFT are defined (FIG. 10D).

In the state shown in FIG. 10D, the active layer of the P-channel TFTconstituting the CMOS circuit has the same structure as the active layerof the N-channel TFT.

Next, as shown in FIG. 11A, a resist mask 936 covering the N-channelTFTs is provided, and an impurity ion for giving a P type (boron is usedin this embodiment) is added.

Although this step is also divided and is carried out two times like theforegoing adding step of the impurity, since the N-channel type must beinverted into the P-channel type, the B (boron) ion with a concentrationseveral times the foregoing addition concentration of the P ion isadded.

In this way, a source region 937, a drain region 938, a lowconcentration impurity region 939, and a channel formation region 940 ofthe P-channel TFT constituting the CMOS circuit are formed (FIG. 11A).

After the active layer is completed in the manner as described above,activation of the impurity ions is made by combination of furnaceannealing, laser annealing, lamp annealing, and the like. At the sametime, damages of the active layers caused in the adding steps arerepaired.

Next, as an interlayer insulating film 941, a laminated film of asilicon oxide film and a silicon nitride film is formed. Next, aftercontact holes are formed in the interlayer insulating film, sourceelectrodes 942, 943 and 944, and drain electrodes 945 and 946 are formedto obtain the state shown in FIG. 11B. An organic resin film may be usedas the interlayer insulating film 941.

After the state shown in FIG. 11B is obtained, a first interlayerinsulating film 947 made of an organic resin film and having a thicknessof 0.5 to 3 μm is formed. Polyimide, acryl, polyimide amide, or the likemay be used for the organic resin film. The merits of using the organicresin film are listed as follow: a film forming method is simple; a filmthickness can be easily increased; parasitic capacitance can be reducedsince its relative dielectric constant is low; and flatness isexcellent. An organic resin film other than the above may be used.

Next, a black matrix 948 made of a film having shading properties andhaving a thickness of 100 nm is formed on the first interlayerinsulating film 947. Although a titanium film is used as the blackmatrix 948 in this embodiment, a resin film including black pigments, orthe like may be used.

In the case where the titanium film is used for the black matrix 948,part of wiring lines of a driving circuit or other peripheral circuitportions can be formed of titanium. The wiring lines of titanium can beformed at the same time as the formation of the black matrix 948.

After the black matrix 948 is formed, a second interlayer insulatingfilm 949 made of one of a silicon oxide film, a silicon nitride film,and an organic resin film, or a laminated film thereof and having athickness of 0.1 to 0.3 μm is formed. A contact hole is formed in theinterlayer insulating film 947 and the interlayer insulating film 949,and a pixel electrode 950 with a thickness of 120 nm is formed.According to the structure of this embodiment, auxiliary capacitance isformed at a region where the black matrix 948 overlaps with the pixelelectrode 950 (FIG. 11C). Since this embodiment relates to atransmission type active matrix liquid crystal display device, atransparent conductive film of ITO or the like is used as a conductivefilm forming the pixel electrode 950.

Next, the entire of the substrate is heated in a hydrogen atmosphere ata temperature of 350° C. for 1 to 2 hours to hydrogenate the entire ofthe device, so that the dangling bonds (unpaired bonds) in the film(especially in the active layer) are compensated. Through the abovesteps, it is possible to manufacture the CMOS circuit and the pixelmatrix circuit on the same substrate.

Next, with reference to FIG. 12, a step of manufacturing an activematrix type liquid crystal display device on the basis of the activematrix substrate manufactured through the above steps will be described.

An oriented film 951 is formed on the active matrix substrate in thestate of FIG. 11C. In this embodiment, polyimide is used for theoriented film 951. Next, an opposite substrate is prepared. The oppositesubstrate is constituted by a glass substrate 952, a transparentconductive film 953, and an oriented film 954.

In this embodiment, such a polyimide film that liquid crystal moleculesare oriented parallel to the substrate is used as the oriented film.Incidentally, after the oriented film is formed, a rubbing process iscarried out so that the liquid crystal molecules are parallel orientedwith a fixed pretilt angle.

Next, the active matrix substrate obtained through the above steps andthe opposite substrate are bonded to each other through a sealingmaterial, a spacer, and the like (not shown) by the well-knowncell-assembly process. Thereafter, a liquid crystal material 955 isinjected between both the substrates, and is completely sealed with asealing agent (not shown). Thus, the transmission type active matrixliquid crystal display device as shown in FIG. 12 is completed.

Various known liquid crystal materials such as twisted nematic liquidcrystal, polymer dispersion liquid crystal, ferroelectric liquidcrystal, anti-ferroelectric liquid crystal, or a mixture offerroelectric and anti-ferroelectric liquid crystals may be used in theliquid crystal display of this example.

In this embodiment, the liquid crystal panel is designed to is makedisplay with a TN (twisted nematic) mode. Thus, a pair of polarizingplates (not shown) are disposed so that the liquid crystal panel is heldbetween the polarizing plates in crossed Nicols (in such a state thatpolarizing axes of the pair of polarizing plates cross each other atright angles).

Thus, it is understood that in this embodiment, display is made in anormally white mode in which the liquid crystal display device becomesin a white display state when a voltage is not applied thereto.

In the liquid crystal panel of this embodiment, the active matrixsubstrate is exposed only at an end surface where an FPC is attached,and other three end surfaces of the active matrix substrate are flushwith those of the opposite substrate.

It is understood that through the above described manufacturing method,in the active matrix type liquid crystal display device of thisembodiment, the driving circuit, other peripheral devices, and pixelscan be integrally formed on the insulating substrate such as a quartzsubstrate or a glass substrate.

FIG. 13 shows the active matrix type liquid crystal display devicemanufactured by the foregoing manufacturing method. FIG. 13 shows theouter appearance of the active matrix type liquid crystal display devicewhen a check pattern is displayed.

Although the active matrix type liquid crystal display device shown inFIG. 13 displays a black and white check pattern, when three such activematrix type liquid crystal display devices are used, a full colorprojection type liquid crystal display device can be realized.

Here, the features of the crystal structure of the lateral growth regionof the semiconductor layer obtained through the manufacturing method ofthis embodiment will be described.

The lateral growth region formed in accordance with the foregoingmanufacturing method has microscopically a crystal structure in which aplurality of rod-like (or flattened rod-like) crystals are arranged inalmost parallel to each other and with regularity to a specificdirection. This can be easily ascertained by observation with a TEM(Transmission Electron Microscope).

The present inventors observed the crystal grain boundaries of thesemiconductor thin film obtained through the foregoing manufacturingmethod in detail by an HR-TEM (High Resolution Transmission ElectronMicroscope) (FIG. 14). In the present specification, the crystal grainboundary is defined as a grain boundary formed at an interface wheredifferent rod-like crystals are in contact with each other, unlessspecified otherwise. Thus, the crystal grin boundary is regarded asdifferent from, for example, a macroscopic grain boundary formed bycollision of separate lateral growth regions.

The foregoing HR-TEM (High Resolution Transmission Electron Microscope)is a method in which a sample is vertically irradiated with an electronbeam and the arrangement of atoms and molecules is estimated by usinginterference of transmission electrons or elastically scatteredelectrons. By using this method, it is possible to observe the state ofarrangement of crystal lattices as lattice stripes. Thus, by observingthe crystal grain boundary, it is possible to infer the bonding state ofatoms at the crystal grain boundary.

In the TEM photograph (FIG. 14) obtained by the present inventors, thestate where two different crystal grains (rod-like crystal grains) arein contact with each other at the crystal grain boundary is clearlyobserved. At this time, it is ascertained by the electron beamdiffraction that the two crystal grains are almost in a {110}orientation although some deviations are included in crystal axes.

In the observation of lattice stripes by the TEM photograph as describedabove, lattice stripes corresponding to a {111} plane are observed inthe {110} plane. Incidentally, the lattice stripe corresponding to the{111} plane indicates such a lattice stripe that when crystal grain iscut along the lattice stripe, the {111} plane appears in the section. Itis possible to simply ascertain through the distance between the latticestripes to what plane the lattice stripe corresponds.

At this time, the present inventors observed in detail the TEMphotograph of the semiconductor thin film obtained through the foregoingmanufacturing method, and as a result, very interesting findings wereobtained. In both of the two different crystal grains seen in thephotograph, lattice stripes corresponding to the {111} plane were seen.And it was observed that the lattice stripes were obviously parallel toeach other.

Further, irrespective of the presence of the crystal grain boundary,lattice stripes of the two different crystal grains were connected toeach other so as to cross the crystal grain boundary. That is, it wasascertained that almost all lattice stripes observed to cross thecrystal grain boundary were linearly continuous in spite of the factthat they were lattice stripes of different crystal grains. This is alsothe case with any crystal grain boundary.

Such a crystal structure (precisely the structure of crystal grainboundary) indicates that two different crystal grains are in contactwith each other with excellent conformity in the crystal grain boundary.That is, crystal lattices are continuously connected to each other inthe crystal grain boundary, so that such a structure is formed that traplevels caused by crystal defects or the like are not easily formed. Inother words, it can be said that the crystal lattices are continuous inthe crystal grain boundary.

In FIG. 15, for reference, analysis by the electron beam diffraction andHR-TEM observation was carried out by the present inventors for aconventional polycrystalline silicon film (so-called high temperaturepolysilicon film) as well. As a result, it was found that latticestripes were random in the two different crystal grains and there hardlyexisted connection continuous in the crystal grain boundary withexcellent conformity. That is, it was found that there were manyportions where the lattice stripes were cut in the crystal grainboundary, and there were many crystal defects.

The present inventors refer to the bonding state of atoms in the casewhere the lattice stripes correspond to each other with good conformity,like the semiconductor thin film produced by the method of the presentembodiment, as “paired bond,” and refer to a bond at that time as a“paired bond.” On the contrary, the present inventors refer to thebonding state of atoms in the case where the lattice stripes do notcorrespond to each other with good conformity, often seen in aconventional polycrystalline silicon film, as “unpaired bond,” and referto a bond at that time as an “unpaired bond” (or an “dangling bond”).

Since the semiconductor thin film used in the present embodiment isextremely excellent in conformity at the crystal grain boundary, theforegoing unconformity bonds are very few. As a result of study forarbitrary plural crystal grain boundaries conducted by the presentinventors, the existing ratio of the unconformity bonds to the totalbonds was 10% or less (preferably 5% or less, more preferably 3% orless). That is, 90% or more of the total bonds (preferably 95% or more,more preferably 97% or more) are constituted by the conformity bonds.

FIG. 16A shows a result of observation by the electron beam diffractionfor a lateral growth region formed in accordance with the foregoingsteps. FIG. 16B shows an electron beam diffraction pattern of aconventional polysilicon film (called “high temperature polysiliconfilm”) observed for comparison.

In the electron beam diffraction patterns shown in FIGS. 16A and 16B,the diameter of an irradiation area of an electron beam is 4.25 μm, andthe information of a sufficiently wide region is collected. Thephotographs shown here show typical diffraction patterns as a result ofinvestigation for arbitrary plural portions.

In the case of FIG. 16A, diffraction spots (diffraction flecks)corresponding to the <110> incidence appear comparatively clearly, andit can be ascertained that almost all crystal grains in the irradiationarea of the electron beam are in the {110} orientation. On the otherhand, in the case of the conventional high temperature polysilicon filmshown in FIG. 16B, clear regularity can not be seen in the diffractionspots, and it is found that grain boundaries with plane orientationother than the {110} plane are irregularly mixed.

Like this, the feature of the semiconductor thin film used in thepresent invention is that this film shows the electron beam diffractionpattern having regularity peculiar to the {110} orientation, althoughthis film is a semiconductor thin film having crystal grain boundaries.When electron beam diffraction patterns are compared, the differencefrom the conventional semiconductor thin film is clear.

As described above, the semiconductor thin film manufactured through theforegoing manufacturing steps is a semiconductor thin film having acrystal structure (precisely a structure of a crystal grain boundary)quite different from the conventional semiconductor thin film. Thepresent inventors have explained the result of analysis as to thesemiconductor thin film used in this embodiment in Japanese PatentApplication Nos. Hei 9-55633 filed on Feb. 24, 1997, Hei 9-165216 filedon Jun. 6, 1997 and Hei 9-212428 filed on Jul. 23, 1997 as well. Theentire disclosures of the three Japanese Patent Applications includingspecification, claims, drawings and summary, respectively areincorporated herein by references in their entirety.

Since 90% or more of the crystal grain boundaries of the semiconductorthin film used in the present invention as described above areconstituted by conformity bonds, they hardly have a function as abarrier against movement of carriers. That is, it can be said that thesemiconductor thin film used in this embodiment has substantially nocrystal grain boundary.

In the conventional semiconductor thin film, although the crystal grainboundary serves as a barrier for blocking the movement of carriers,since such a crystal grain boundary does not substantially exist in thesemiconductor thin film used in the present invention, a high carriermobility can be realized. Thus, the electrical characteristics of a TFTmanufactured by using the semiconductor thin film used in thisembodiment show very excellent values. This will be described below.

[Findings as to Electrical Characteristics of a TFT]

Since the semiconductor thin film used in this embodiment can beregarded substantially as single crystal (crystal grain boundaries donot exist substantially), a TFT using the semiconductor thin film as anactive layer shows electrical characteristics comparable with a MOSFETusing single crystal silicon. Data as shown below have been obtainedfrom TFTs experimentally formed by the present inventors.

(1) The subthreshold coefficient as an index showing switchingperformance (promptness in switching of on/off operation) of a TFT is assmall as 60 to 100 mV/decade (typically 60 to 85 mV/decade) for both anN-channel TFT and a P-channel TFT.

(2) The field effect mobility (μ_(FE)) as an index showing an operationspeed of a TFT is as large as 200 to 650 cm²/Vs (typically 250 to 300cm²/Vs) for an N-channel TFT, and 100 to 300 cm²/Vs (typically 150 to200 cm²/Vs) for a P-channel TFT.

(3) The threshold voltage (V_(th)) as an index indicating a drivingvoltage of a TFT is as small as −0.5 to 1.5 V for an N-channel TFT and−1.5 to 0.5 V for a P-channel TFT.

As described above, it has been ascertained that extremely superiorswitching characteristics and high speed operation characteristics canbe realized.

Incidentally, in the formation of CGS, the foregoing annealing step at atemperature (700 to 1100° C.) above crystallizing temperature plays animportant role with respect to lowering of defects in the crystalgrains. This will be described below.

FIG. 17A is a TEM photograph of a crystal silicon film when steps up tothe foregoing crystallization step have been ended, which is magnified250 thousand times. Zigzag defects as indicated by an arrow areascertained in the crystal grains (black portion and white portionappear due to the difference of contrast).

Although such defects are mainly lamination defects in which the orderof lamination of atoms on a silicon crystal lattice plane is discrepant,there is also a case of dislocation. It appears that FIG. 17A shows alamination defect having a defect plane parallel to the {111} plane.This can be ascertained from the fact that the zigzag defects are bentat about 70°.

On the other hand, as shown in FIG. 17B, in the crystal silicon filmused in the present invention, which is enlarged at the samemagnification, it is ascertained that defects caused by laminationdefects, dislocations, and the like are hardly seen, and thecrystallinity is very high. This tendency can be seen in the entire ofthe film surface, and although it is difficult to eliminate the defectsin the present circumstances, it is possible to decrease the number tosubstantially zero.

That is, in the crystal silicon film used in this embodiment, defects inthe crystal grain are reduced to such an extent that the defects can bealmost neglected, and the crystal grain boundary can not become abarrier against movement of carriers because of its high continuity, sothat the film can be regarded as single crystal or substantially singlecrystal.

Like this, in the crystal silicon films shown in the photographs ofFIGS. 17A and 17B, although both of the crystal grain boundaries havealmost equal continuity, there is a large difference in the number ofdefects in the crystal grains. The reason why the crystal silicon filmshown in FIG. 17B shows electrical characteristics much higher than thecrystal silicon film shown in FIG. 17A is mainly the difference in thenumber of defects.

From the above, it is understood that the gettering process of anelement for facilitating crystallization of the amorphous silicon filmis an indispensable step in the formation of CGS. The present inventorsconsider the following model for a phenomenon caused by this step.

First, in the state shown in FIG. 17A, the element for facilitatingcrystallization of the amorphous silicon film (typically nickel) issegregated at the defects (mainly lamination defects) in the crystalgrain. That is, it is conceivable that there are many bonds such asSi-Ni-Si.

However, when Ni existing in the defects is removed by carrying out thegettering process of the element for facilitating crystallization of theamorphous silicon film, the bond of Si-Ni is cut. Thus, the remainingbond of silicon immediately forms Si-Si bond and becomes stable. In thisway, the defects disappear.

Of course, although it is known that the defects in the crystal siliconfilm disappear by thermal annealing at a high temperature, it ispresumed that since bonds with nickel are cut and many unpaired bondsare produced, so that recombination of silicon is smoothly carried out.

The present inventors also consider a model in which the crystal siliconfilm is bonded to its under layer by a heat treatment at a temperature(700 to 1100° C.) above the crystallizing temperature and adhesivenessis increased, so that the defects disappear.

The thus obtained crystal silicon film (FIG. 17B) has the feature thatthe number of defects in the crystal grains is extremely smaller thanthe crystal silicon film (FIG. 17A) in which merely crystallization hasbeen carried out. The difference in the number of defects appears as thedifference in spin density by the analysis of Electron Spin Resonance(ESR). In the present circumstances, the spin density of the crystalsilicon film used in the present invention is at most 1×10¹⁸ spins/cm³(typically, 5×10¹⁷ spins/cm³ or less).

The crystal silicon film having the above described crystal structureand the features and used in the present invention is referred to as“Continuous Grain Silicon: CGS.”

EMBODIMENT 2

In the foregoing embodiment 1, description has been made on the casewhere the digital driving system driving circuit of the presentinvention is used for the active matrix type liquid crystal displaydevice. In this case, as a display method used for the active matrixtype liquid crystal display device, a TN mode using a nematic liquidcrystal, a mode using electric field control birefringence, a mixedlayer of a liquid crystal and a high polymer, a so-called polymerdispersion mode, and the like can also be used.

Further, in the digital driving system driving circuit of the presentinvention, the line-sequential scanning of the pixel TFTs is carried outas described above, and the number of pixels corresponds to the futureATV (Advanced TV). Thus, if the driving circuit is used for an activematrix type liquid crystal display device which uses a liquid crystalwith a high response speed, that is, a so-called non-thresholdantiferroelectric liquid crystal, more excellent characteristics can beshown.

The driving circuit of the present invention can also be used for aliquid crystal display device using a ferroelectric liquid crystal whichis being realized by recent researches and in which the orientation ofthe ferroelectric liquid crystal is controlled with a specific orientedfilm and gradation display can be made like a TN liquid crystal mode.

The driving circuit of the present invention shown in the embodiment 1or 2 may be used as a driving circuit of a display device including anyother display medium in which its optical characteristics can bemodulated in response to an applied voltage. For example, the drivingcircuit may be used as a driving circuit of a display device using anelectroluminescence element or the like.

The driving circuit of the present invention typically shown in theembodiment 1 or 2 may be used as a driving circuit of a semiconductordevice such as an image sensor. In this case, the driving circuit canalso be applied to such an image sensor that a light receiving portionof the image sensor and a picture display portion for displaying apicture converted into electric signals at the light receiving portionare integrally formed. The image sensor to which the present inventionis applied may be a line sensor or an area sensor.

EMBODIMENT 3

In the embodiments 1 and 2, although a transmission type active matrixliquid crystal display device has been described, it is needless to saythat the driving circuit of the present invention can also be used for areflection type active matrix liquid crystal display device.

EMBODIMENT 4

The driving circuit of the embodiment 1, and the active matrix typesemiconductor display device (embodiments 2 and 3) using the drivingcircuit have various applications. In this embodiment, semiconductordevices each including such a semiconductor display device will bedescribed.

As such semiconductor devices, a video camera, a still camera, aprojector, a head mount display, a car navigation system, a personalcomputer, a portable information terminal (mobile computer, portablephone, etc.) and the like are enumerated. Examples of those will beshown in FIGS. 18A to 18F.

FIG. 18A shows a portable telephone which is constituted by a main body1801, an audio output portion 1802, an audio input portion 1803, asemiconductor display device 1804, an operation switch 1805, and anantenna 1806.

FIG. 18B shows a video camera which is constituted by a main body 1901,a semiconductor display device 1902, an audio input portion 1903, anoperation switch 1904, a battery 1905, and an image receiving portion1906.

FIG. 18C shows a mobile computer which is constituted by a main body2001, a camera portion 2002, an image receiving portion 2003, anoperation switch 2004, and a semiconductor display device 2005.

FIG. 18D shows a head mount display which is constituted by a main body2101, a semiconductor display device 2102, and a band portion 2103.

FIG. 18E shows a rear type projector which is constituted by a main body2201, a light source 2202, a semiconductor display device 2203, apolarizing beam splitter 2204, reflectors 2205 and 2206, and a screen2207. Incidentally, in the rear type projector, it is preferable that anangle of the screen can be changed, while fixing the main body,according to the position where a viewer sees the screen. When threesuch semiconductor display devices 2203 (each being made to correspondto light of R, G, and B) are used, it is possible to realize a rear typeprojector with higher resolution/higher fineness.

FIG. 18F shows a front type projector which is constituted by a mainbody 2301, a light source 2302, a semiconductor display device 2303, anoptical system 2304, and a screen 2305. When three such semiconductordisplay devices 2303 (each being made to correspond to light of R, G,and B) are used, it is possible to realize a front type projector withhigher resolution/higher fineness.

As described above, according to the present invention, in a drivingcircuit of a semiconductor display device, the fluctuation of itscharacteristics can be reduced while securing the current capacity of abuffer circuit. Thus, the semiconductor display device without displayblur (display unevenness) and with high fineness/high resolution can berealized.

1. A portable telephone having a display device, said display devicecomprising: a source signal line side driving circuit; and a gate signalline side driving circuit, wherein said gate signal line side drivingcircuit includes a buffer circuit connected with an output line from ashift register circuit, said buffer circuit having a plurality ofinverters, wherein each of said inverters comprises a plurality ofn-channel thin film transistors and a plurality of p-channel thin filmtransistors, and wherein each of said plurality of n-channel thin filmtransistors is connected in parallel with each other and each of saidplurality of p-channel thin film transistors is connected in parallelwith each other.